The two men had been attacking a detachment of Islamic State fighters in the Homs region on Friday, when the Syrian Mi-25 helicopter they were in ran out of ammunition, the ministry said, according to Interfax.

“The turning helicopter was hit by militants’ gunfire from the ground and crashed in the area controlled by the Syrian government army. The crew died," it added.

Video footage published on Saturday by Islamic State’s affiliated news agency Amaq showed a helicopter being shot and crashing to the ground against cries of 'It's fallen, God is greatest'.

Russian forces entered the conflict at the end of last year, backing the forces of Syrian President Bashar al-Assad.